In a conventional injection molding apparatus, resin pellets are previously dried for some days by a drier of a predetermined temperature. The resin pellets are thus turned into a predetermined dried condition. While they are dried, water in the resin pellets is reduced to a predetermined value. The dried pellets with water of the predetermined value are thrown into the injection molding apparatus. In other words, the water in the resin pellets is carefully controlled before they are thrown into the injection molding apparatus.
An injection molding product has blowholes. This means that the conventional drying method is insufficient. It is considered that they are caused by water generated from chemical combinations of resin ingredients in pellets due to heating. Resin materials which constitute pellets and chemicals which are used for plasticizer generate vapor and gas due to heating. Chemicals in pellets are generated as poisonous gas in the process of melting in the injection molding apparatus. The generated poisonous gas is discharged into the atmosphere.
In these days, it is an issue of wide importance that human bodies are influenced by harmful objects, especially objects that distract internal secretion (environmental hormone), included in plastic. It is therefore socially important to prevent discharging these poisonous materials into the atmosphere.
This invention was made to solve the foregoing problems, and is aimed to remove harmful objects generated when resin pellets are melted in the injection molding apparatus, improve the quality of the products, reduce the inferior goods for at least 20% than before, and reduce frequency of maintenance for cleaning the inside of the die. Consequently, the productivity is increased and the electric energy required for injection molding is considerably decreased.